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(h)
Grinding mill
.—Model ZM200 rotor mill (Retsch, Haan, Germany), or equivalent.
B.
Reagents
(a)
Ammonium citrate, dibasic
.—(NH
4
)
2
HC
6
H
5
O
7
, formula weight (FW) 226.19, ACS grade,
purity >98% (EMD Chemicals, Darmstadt, Germany).
(b)
EDTA, disodium salt, dihydrate
.—C
10
H
14
N
2
Na
2
O
8
·2H
2
O, FW 372.24, purity > 99% (J.T.
Baker Chemicals, Center Valley, PA).
(c)
Ammonium hydroxide
.—NH
4
OH, FW 35.05, 28.0–30.0% as NH
3
(Mallinckrodt
Chemicals, Center Valley, PA).
(d)
Nitric acid
.—HNO
3
, 67–70%, OmniTrace grade (EMD Chemicals).
(e)
Potassium dihydrogen phosphate
.—KH
2
PO
4
, certified at 22.73% P and 28.73% K,
National Institute of Standards and Technology (NIST) 200a (Gaithersburg, MD),
www.nist.gov/srm.(f)
Potassium chloride
.—KCl, FW 74.55, ACS grade, purity >99% (Mallinckrodt Chemicals).
(g)
Potassium nitrate
.—KNO
3
, certified at 38.66% K, NIST 193.
(h)
Triton X-100
.—Octylphenol ethoxylate (J.T. Baker Chemicals).
(i)
10, 000
μ
g/mL Be standard
.—In 4% HNO
3
, product 10M5-1 (High Purity
Standards, Charleston, SC).
(j)
10,000
μ
g/mL Sc standard
.—In 4% HNO
3
, product 10M48-1 (High Purity Standards).
(k)
Cesium chloride
.—CsCl, FW 168.36, purity > 99.999% (Sigma-Aldrich, St. Louis, MO).
(l)
Lithium nitrate
.—LiNO
3
, FW 68.95, purity > 99%, (EM Science, Gibbstown, NJ).
(m)
Citrate
–
EDTA extraction solution (0.11 M ammonium citrate and 0.033 M disodium
EDTA)
.—Weigh and completely transfer 25 g disodium EDTA [(
b
) above] and 50 g dibasic
ammonium citrate [(
a
) above] to a 2 L volumetric flask containing approximately 1500 mL
deionized (or equivalent) water. Adjust the pH to near neutral by adding 30 mL of (1 + 1, v/v)
ammonium hydroxide [(
c
) above] –water solution in a fume hood. Adjust the final pH to 7.00
(±0.02) using a pH electrode [Alternative A, A (
b
)] and meter [Alternative A, A (
c
)] while adding
the ammonium hydroxide–water (1 + 1, v/v) solution drop-by-drop and stirring. After obtaining
a stable pH of 7.00 (±0.02), bring the flask to volume with deionized water and mix. Larger
volumes of this solution can be prepared; however, it is susceptible to microbial degradation
resulting in a maximum shelf life of 2 weeks, if stored in a dark location.
(n)
0.5% Triton-X
.—Add 1 mL Triton X-100 [(
h
) above] to a 200 mL volumetric flask and dilute to
volume with deionized water.
(o)
Internal standard/ionization buffer (10 µg/mL Sc in 0.018 M CsCl and 4% nitric acid).
—
Candidates for 2016 Method of the Year
246